Director's Research Group

The Director's Research Group aims at understanding terrestrial biosphere feedback processes in the Earth's climate system. How do these processes cause accelerating changes into new climate and ecosystem states? How strong is the effect of terrestrial biosphere feedback processes on climate change and variability in comparison with other feedback processes? And how strong is the synergy between feedbacks? These questions are mainly raised in connection with palaeoclimate change, with a focus on the Sahara and the Arabian deserts in close cooperation mainly with the groups Climate-Biosphere Interactions and Global Vegetation Modelling and with external partners.

(Graphic credit: Dominique Donoval, MPI-M)

Plant diversity of ecosystems in arid environment like Sahara and Sahel has changed over the past several thousand years. A mathematical model suggests that plant diversity may stabilise climate – ecosystem interaction thereby leading to more gradual, fluctuating decline of taxa (coloured lines), instead of abrupt vegetation and precipitation change. (Claussen et al., Nature Geoscience, 6, 2013).

Selected Research Projects

Saharan landscape dynamics and abrupt changes in marine sediment records: Marine sediment records reveal an abrupt and strong increase in dust deposition in the North Atlantic at the end of the African Humid Period some 4.9 to 5.5 ky ago. The change in dust flux has been attributed to varying Saharan land surface cover or, alternatively, to enhanced surface winds and intensification of coastal upwelling. For the first time, we have been able to demonstrate the direct link between dust accumulation in marine cores and changes in Saharan land surface using the coupled atmosphere-aerosol model ECHAM6-JSBACH-HAM2.See Egerer et al., 2016, 2017 in the list of publications

Exploring effects of plant diversity on the stability of atmosphere -- vegetation interaction in semi-arid regions: The proposition that plant diversity can significantly affect the stability of the atmosphere-vegetation interaction at the end of the African Humid Period has been critically re-assessed. Paleo data of biodiversity in Northern Africa have been analysed and the conceptual model has been applied to the data. It appears that in principle the proposition is valid to explain that ecosystems high in plant diversity are less prone to abrupt changes than ecosystems poor in plant diversity. New simulations with JSBACH and the MPI-ESM demonstrate that not the mere number of plant functional types determine the dynamics of atmosphere-vegetation interaction in semi-arid regions, but rather the quality of PFTs. If shrubs are excluded from the PFTs in JSBACH, then the simulated Holocene expansion of the Sahara appears to be much faster than in simulations with all PFTs considered.See Claussen et al., 2013; Groner et al., 2016; Groner 2017 in the list of publications

Biogeographic dynamics in different climates and different atmospheric CO2 concentrations:To date, the transitivity of the global system has been analysed for the late Quaternary (glacial, interglacial, and present-day) climate. We have extended this analysis to a warm, almost ice-free climate with a different configuration of continents for which we chose the early Eocene climate as a role model. It appears that with initially deserted continents, an extended desert in central Asia, the so-called Tarim desert, forms in the simulations with our MPI-ESM. With initially forested continents the Tarim desert is much smaller while coastal deserts develop along the west coast of the Americas. These differences can be attributed to shifts in the large-scale tropical circulation triggered by climate - vegetation interaction. Further analyses show that local feedback processes are less important in the development of multiple states in early Eocene climate. In the interglacial, pre-industrial climate, on the contrary, multiple states develop only in the Sahel region presumably triggered by local climate - vegetation interaction.See Port and Claussen, 2015 in the list of publications